1. Field of the Invention
This invention relates to a pyroelectric infrared detector, and more particularly to an infrared ray receiving element in which temperature drift in incoming signals and noise caused by vibration can be eliminated by defining a plurality of pyroelectric operating areas, utilizing one of the operating areas an an infrared signal detection area, and compensating for the electrical signals generated in the signal detection area by using the electrical signals generated in another pyrolectric operating area.
2. Description of the Prior Art
It is well known that a pyroelectric property can be provided by polarizing a high molecular weight film such as, for example, a polymer or copolymer consisting essentially of a vinylidene fluoride, a vinyl fluoride, and an ethylene trifluoride or the other polar monomers. Various kinds of infrared detectors such as fire alarms or intrusion alarms using such a pyroelectric film have been proposed. However, since the high molecular weight pyroelectric film, in general, has a pyroelectric as well as a pyroelectric properties, it generates an electrical signal due to external vibration, the external vibration often becomes a cause of large noises. In order to eliminate these noises, U.S. Pat. No. 3,877,308, for example, has proposed a pyroelectric element constituted by disposing a plurality of pyroelectric operating areas with electrodes on both surfaces of a sheet of high molecular pyroelectric film. The element utilizes only one of these pyroelectric operating areas for infrared signal detection for radiant heat from the outside. The detection area is coupled with at least one of the remaining pyroelectric operating areas through respective electrodes of different polarities. The pyroelectric signals resulting only from radiant heat can be obtained by compensating for the electrical signal generated in the signal detection areas with the electrical signals generated in another pyroelectric operating area.
In cases where such a specific pyroelectric operating area is used for noise compensation as mentioned above, it is preferable that the quantity and quality of noises due to environmental conditions surrounding the pyroelectric operating areas for detection and compensation be equal as much as possible. However, in the case of the U.S. Pat. No. 3,877,308, the aforesaid conditions are not sufficient since the pyroelectric operating area for compensation is not disposed at a place where it is influenced by radiant heat. Accordingly, where comparatively strong radiant heat is to be detected by means of a pyroelectric element having a low sensitivity, the compensation for the element disclosed in the U.S. patent is effective, but there is a large amount of noise due to the temperature drift when the sensitivity of the pyroelectric element is increased.
In addition, in the U.S. Pat. No. 3,453,432, there is proposed an infrared detector comprising pyroelectric operating areas such that radiant heat falls on a sheet of pyroelectric material located within the infrared detector. A light-reflective electrode such as aluminum is disposed on the light receiving surface side of one operating area which a light-absorptive electrode such as gold black, for example, is disposed on the light receiving surface side of the other operating area. The operating area having the light-absorptive electrode serves as a detection element and the operating area having the light-reflective electrode serves as a compensation element. In this U.S. patent, since an inorganic substance such as ceramic and the like, for example, is used as pyroelectric material, and the two pyroelectric operating areas are both located within a region into which the radiant rays are entered, it can be expected that the noises due to environmental conditions will be further decreased. It is, however, further desired to provide a lower noise and driftless device.